1. Field of the Invention
The present invention relates to an acceleration sensor and a disk drive employing the acceleration sensor. More particularly, the present invention is concerned with an acceleration sensor to be adapted as a high-precision positioning control means for a head actuator, and a disk drive employing the acceleration sensor.
2. Description of the Related Art
In the past, an acceleration sensor has been employed in a head actuator, which is included in a disk drive such as a magnetic disk drive, as a means for controlling the position of a head very precisely. A high-precision positioning control method using the acceleration sensor included in the disk drive is, for example, disclosed in “Multi-sensing head Positioning Control using Carriage Acceleration Information” (Collected Papers published from the Japan Society of Mechanical Engineers, No. 97-1, 1997, pp. 404–405). The Collected Papers include proposals for improving precision in positioning a head, wherein an output of an acceleration sensor, representing the acceleration of a motion made by a carriage and which is detected by the acceleration sensor, is fed back in order to expand a controllable frequency band. Moreover, a control method has been proposed where: a disturbance is inferred from the acceleration of a motion made by a carriage which is detected by an acceleration sensor and the magnitude of a current flowing through a voice coil motor (VCM) that is used to drive a head actuator; and a current canceling the disturbance is added to a sustaining current required for the head actuator in order to suppress the disturbance.
However, as long as positioning of a head is controlled based on an acceleration detected by an acceleration sensor, the acceleration sensor requires an input of a high signal-to-noise ratio so as to detect the acceleration. In general, as an added mass increases, the inertia of a piezoelectric acceleration sensor against an acceleration is intensified. Therefore, a weight that has a large mass is attached to a sensor element so that the sensor element will be readily deformed and a large output, representing a detected acceleration, can be provided. However, when the acceleration sensor is mounted in a carriage included in a disk drive, the motion of a head actuator is slowed by the increase in added mass. This causes a problem that the seek speed at which a head is positioned may decrease. Moreover, the increase in the added mass may bring about a drop in a resonant frequency of a carriage arm. Therefore, a large mass cannot be added, in practice.